1. Field of the Invention
The invention relates to a method of manufacturing semiconductor devices whereby first a Ti layer and then a TiN layer is deposited on slices of semiconductor material by placing the slices on a support one after the other in a deposition chamber, which support is arranged opposite a target of Ti surrounded by an annular anode, material is then sputtered off the target by means of a plasma which is generated near the target in Ar during the deposition of the Ti layer, and in a gas mixture of Ar and N.sub.2 during the deposition of the TiN layer. The target is cleaned in an additional process step by sputtering off material therefrom by means of a plasma generated in Ar each time before a next slice is placed in the chamber.
2. Description of the Related Art
In modern IC technology, a metallization comprising a Ti layer, a TiN layer and a further conductive layer is often provided on a surface of a semiconductor body. The Ti layer serves to obtain a good adhesion and a low contact resistance between the metallization and the semiconductor body. When a layer of Al or of Al alloyed with a few percent of Si or Cu is used as the conductive top layer, the TiN layer serves as a barrier to prevent chemical reactions of the Al with the Ti and the semiconductor material situated underneath the barrier layer. When W is used as a conductive top layer, deposited by means of a usual CVD process (chemical deposition process) for which WF.sub.6 is used, the TiN serves as a barrier to prevent chemical reactions between Ti and F which is formed during such a CVD process.
The depositions are carried out in practice on slices of semiconductor material which are broken or sawn into a large number of separate semiconductor chips at a later stage. A slice is passed through an input station into a first deposition chamber of a sputter deposition device, where the Ti and TiN layers are deposited by the method described above, after which the slice is transported to a second deposition chamber in which, for example, an Al or W layer is deposited, and finally the slice is taken from the device through an output station. When a slice leaves a deposition chamber, a new slice is immediately introduced into the chamber in practice.
During the deposition of the TiN layer, a plasma is generated in a gas mixture comprising Ar and N.sub.2 near the Ti target. A top layer comprising nitrogen is created thereby on the target during this deposition step. Material is sputtered off this target during the extra process step, which material is then deposited on the slice. Thus a Ti layer comprising nitrogen is deposited on the slice, which layer initially consists of TiN and in which the nitrogen occurs in a decreasing concentration seen in the thickness direction of the layer. The layer accordingly merges well with the underlying TiN layer. If such a layer were instead deposited on the next succeeding slice instead of the Ti layer as a first layer of a metallization, then this metallization thereon would on the contrary exhibit a bad adhesion and a high contact resistance.
"Eclipse Newsletter", 10, Jun./Jul. 1992, discloses a method of the kind mentioned in the opening paragraph whereby the additional process step is continued for some time after cleaning of the target, so that another layer of pure Ti is deposited on the slice in addition to the Ti layer comprising nitrogen. This pure Ti layer serves to obtain a good adhesion with a further Al layer to be provided.
It is achieved by the known method that the layer deposited as a first layer on a slice has a good adhesion thereto and a low contact resistance because this layer consists of pure Ti owing to cleaning of the target. The known method has the disadvantage, however, that a further layer comprising free Ti is deposited on top of the TiN layer. If a conductive top layer of Al or Al alloyed with a few percents of Si or Cu is provided thereon, the Al and Ti react with one another, forming compounds with a comparatively high electric resistance. A good adhesion is then indeed obtained, but the conductive Al layer must then be provided to a comparatively great thickness in order to ensure that conductor tracks having a comparatively low resistance can be formed in the layer structure thus created. If a W layer is deposited on the said layer comprising free Ti by means of a usual CVD process (chemical deposition process) in which WF.sub.6 is used, then the free Ti reacts with F formed during such a CVD process. This leads to the formation of TiF.sub.3, to which W has a bad adhesion.